An engine may include an actuator for changing the engine's compression ratio. By changing the engine's compression ratio, it may be possible to improve engine efficiency. In one example, a lower compression ratio may be provided in the engine at higher engine speeds and loads to reduce the possibility of engine knock. A higher compression ratio may be provided in the same engine at lower engine loads to increase engine efficiency when the possibility of engine knock is lower. The compression ratio may be set to an intermediate value that is between the high compression ratio and the low compression ratio when the engine is operated at intermediate load levels. However, even with variable compression, the engine may knock during some conditions. Therefore, it may be desirable to provide a way of reducing a possibility of engine knock for a variable compression ratio engine that includes an actuator to adjust the engine's compression ratio.
The inventors herein have recognized the above-mentioned issues and have developed an engine operating method, comprising: adjusting an engine's compression ratio via a controller responsive to present engine speed and engine load; forecasting a shifting of a transmission from a first gear to a second gear via the controller; and adjusting an engine's compression ratio via the controller responsive to an engine speed and engine load based on the forecasted shifting of the transmission.
By forecasting or predicting when a transmission shift is expected to occur, it may be possible to provide the technical result of reducing the possibility of engine knock that may be related to engine load changing as a result of a transmission gear shift. Specifically, the engine's compression ratio (CR) may be decreased before the transmission is upshifted so that the engine is at a lower compression ratio when the transmission gear shift completes so that an increase in engine load that results from the transmission gear shift may not cause engine knock. Conversely, the engine's compression ratio may be maintained at a lower level until a transmission gear shift is completed when the transmission is downshifted since the engine may operate with the lower compression ratio for a short period of time without engine efficiency degrading substantially.
The present description may provide several advantages. Specifically, the approach may provide improved engine knock control before and after transmission gear shifts. In addition, the approach forecasts or predicts transmission gear shifting events so that a compression ratio device may be operated to improve engine efficiency and mitigate engine knock. Further, the approach may reduce a possibility of driveline torque disturbances that may be caused by operating a compression ratio changing device while a transmission is shifting between fixed gear ratios.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.